add some c interface COM style stuff

gistfile1.txt

diff --git a/libavdevice/dshow.c b/libavdevice/dshow.c
index ea6c21c..7694f05 100644
--- a/libavdevice/dshow.c
+++ b/libavdevice/dshow.c
@@ -574,6 +574,61 @@ dshow_list_device_options(AVFormatContext *avctx, ICreateDevEnum *devenum,
 
     return 0;
 }
+void SetAudioLatency(IPin *AudioCapturePin, int BufferSizeMilliSeconds);
+void SetAudioLatency(IPin *AudioCapturePin, int BufferSizeMilliSeconds)
+{
+   assert(AudioCapturePin);
+   assert(BufferSizeMilliSeconds > 0);
+
+   // Get the interfaces we need.
+   IAMStreamConfig *config = NULL;
+   if (IPin_QueryInterface(AudioCapturePin, &IID_IAMStreamConfig, (void **) &config) != S_OK) {
+      av_log(NULL, AV_LOG_ERROR, "fail 1");
+        return;
+   }
+
+   IAMBufferNegotiation *bufneg = NULL;
+
+   if (IPin_QueryInterface(AudioCapturePin, &IID_IAMBufferNegotiation, (void **) &bufneg) != S_OK) {
+      av_log(NULL, AV_LOG_ERROR, "fail 2");
+
+        goto end2;
+   }
+
+   // Get the current audio capture properties.
+   AM_MEDIA_TYPE *mt;
+   HRESULT hr = IAMStreamConfig_GetFormat(config, &mt);
+   if (FAILED(hr)) {
+      av_log(NULL, AV_LOG_ERROR, "fail 3");
+      goto end1;
+   }
+
+   assert(*mt->FormatType() == FORMAT_WaveFormatEx);
+   assert(mt->FormatLength() >= sizeof(WAVEFORMATEX));
+   WAVEFORMATEX *wf = (WAVEFORMATEX *)mt->pbFormat;
+
+   // Set the desired buffer size.
+   ALLOCATOR_PROPERTIES props;
+   props.cBuffers = -1;
+   props.cbBuffer = wf->nAvgBytesPerSec * BufferSizeMilliSeconds/1000;
+   props.cbAlign = -1;
+   props.cbPrefix = -1;
+
+   HRESULT got = IAMBufferNegotiation_SuggestAllocatorProperties(bufneg, &props);
+   if (got != S_OK)
+     av_log(NULL, AV_LOG_ERROR, "unable to set smaller audio buffer, got %d", got);
+   else
+     av_log(NULL, AV_LOG_ERROR, "set audio buffer to %dms", BufferSizeMilliSeconds);
+
+   // cleanup
+   // TODO FreeMediaType(*mt);
+   CoTaskMemFree((void *) mt->pbFormat);
+   CoTaskMemFree(mt);
+end1:
+   IAMBufferNegotiation_Release(bufneg);
+end2:
+   IAMStreamConfig_Release(config);
+}
 
 static int
 dshow_open_device(AVFormatContext *avctx, ICreateDevEnum *devenum,
@@ -616,6 +671,9 @@ dshow_open_device(AVFormatContext *avctx, ICreateDevEnum *devenum,
     }
     ctx->capture_filter[devtype] = capture_filter;
 
+    if (devtype == 1)
+      SetAudioLatency((IPin *) device_pin, 50);
+
     r = IGraphBuilder_AddFilter(graph, (IBaseFilter *) capture_filter,
                                 filter_name[devtype]);
     if (r != S_OK) {